1. Field of the Invention
The present invention relates to the field of semiconductor processing and more particularly to a method of preventing delamination of semiconductor layers in a semiconductor device such as a micro-electro-mechanical system (MEMS) device.
2. Discussion of Related Art
Micro-Electro-Mechanical System (MEMS) applications involve the integration of mechanical structures and electronic components on a common silicon wafer or substrate. One particular type of MEMS application is a solid-state memory device that comprises a media substrate bonded to a CMOS substrate. The CMOS substrate consists of an array of MEMS cantilever structures with probe tips that read and write data on the media substrate. The media substrate is made of a phase change or ferroelectric material that can electrically switch between two or more states depending on the amount of electric current received from the probe tip.
Typically, MEMS cantilever structures are fabricated by photolithography and etching of semiconductor, metallic, and insulating layers deposited on the CMOS substrate. The types of materials used for semiconductor layers are usually poly-silicon or silicon-germanium. When depositing semiconductor layers on the CMOS substrate, native oxides tend to form at the interfaces of semiconductor layers. Native oxides refer to silicon oxides that naturally form on the semiconductor layers due to the oxidation of silicon atoms when the CMOS substrate is exposed to oxygen. These native oxides are undesirable because they may react with a buffered oxide etch solution, such as buffered hydrofluoric acid (BHF) solution, and cause delamination of the semiconductor layers. The BHF solution is used to remove gap fill oxide surrounding the semiconductor layers to define the profile of the cantilever structure. This is also known as the cantilever release. Thus, the reaction between the BHF solution and the native oxides may cause delamination of the semiconductor layers. As a result, the entire cantilever structure or some parts of it may lift off from the CMOS substrate.